This invention relates to a laminate and further to a process for producing the laminate. More, particularly, it relates to a laminate having superior properties, for instance, punchability, thermal stability, dimensional stability, mechanical properties, and electrical properties, which comprises at least one inorganic or organic fiber nonwoven fabric impregnated with cyanic acid ester resin composition and at least one glass fabric impregnated with epoxy resin composition, and at least one outermost layer of the laminate being a glass fabric.
2. Description of the Prior Art
Heretofore, there have been known laminates composed of at least one nonwoven fabric and at least one glass fabric as the base materials and the outermost layer being a glass fabric. For example, there may be mentioned a glass fabric-glass paper laminate, a glass fabric-synthetic fiber nonwoven fabric laminate, a glass fabric-glass mat laminate and a glass fiber fabric-paper laminate. IN these conventional laminates there is usually used epoxy resin, phenolic resin, or the like as a resin with which the base material is impregnated, for the purpose of improving punchability and drilling properties. However, the laminates obtained by using prepregs impregnated with such resin have a very large coefficient of thermal expansion in the direction of thickness. In a printed circuit board with plated through-holes made of these laminates, thermal expansion of the board causes a strong stress which is applied to the deposited copper layer of plated through-holes at high temperature and thereby a crack is formed in the metal of the plated through-holes and reliability of the printed circuit board is lowered to a great extent. In addition, thermal expansion coefficients of two base materials in such type of laminates are usually largely different. Since there occurs exfoliation between the glass fabric layer and the nonwoven fabric layer when a plated printed circuit board expands at high temperature, the metal layers of through-holes are broken at the interface between the glass fabric layer and nonwoven fabric layer in which the stress is concentrated. Therefore, these types of laminates are not usually suitable for printed circuit boards with plated through-holes.
Indeed it is possible to lower the thermal expansion coefficient of the laminate by using a high heat resistant type resin as an impregnating resin, but still it is not possible to avoid exfoliation between the base materials and concentration of stress to the metal layer of plated through-holes at the interface portion between the glass fabric layer and nonwoven fabric layer. Further the laminates produced with a high heat-resistant type resin have poor punchability.